April 14, 1899.] 



SCIENCE. 



555 



water. These were the proportious actually 

 emplo5'ed hy Pfeffer and given by Ostwald and 

 others. As compared with the conventional 

 compositiom of a 1 ''/o solution they involve a 

 deficiency of one ninety-ninth part of the sugar, 

 which is far within the limits of error in these 

 investigations ; nor ought they to mislead any 

 body, as the proportions of this kind of per- 

 centicity are explained in the text-books and 

 were given in my paper. 



The departure from the conventional propor- 

 tions of a one-per-cent. solution are not from 

 error nor arbitrary, as the method of compar- 

 ing the osmotic pressure of diflFerent solutions 

 relatively to the gram-molecules of the sub- 

 stances dissolved involves the employment of 

 a uniform quantity of the solvent. 



G. Macloskie. 



Princeton TJniveesity, Jlaroli 25, 1899. 



NOTES ON PSYSICS. 

 WIRELESS TELEGRAPHY. . 



At a recent meeting of the Institution of 

 Electrical Engineers, Marconi described his re- 

 cent work along the lines of wireless telegraphy. 

 In transmitting he uses a 10-inch spark coil and 

 a battery giving about 14 volts and 6 to 8 am- 

 peres. For his spark circuit he uses two ar- 

 rangements, depending upon whether it is 

 necessary to confine the sending of the signals 

 to one direction or not. In the former case 

 cylindrical reflectors are used and capacity is 

 obtained by strips of sheet metal attached to 

 the two spark balls. In the latter case there 

 are no reflectors and one ball is grounded while 

 the other is connected to a vertical wire. A 

 Morse key in the primary circuit makes the 

 signals. The length of the vertical wire de- 

 pends upon the distance to be covered. A wire 

 20 feet high will transmit one mile ; 40 feet, 4 

 miles ; 80 feet, 10 miles approximately ; the 

 distance seems to increase about as the square 

 of the height of the wire. The receiver con- 

 sists of a coherer, or sensitive tube, about four 

 centimeters long, fitted with metallic pole-pieces 

 and partly filled with nickel and silver filings. 

 When not under the action of the radiation the 

 the resistance of this tube is practically infinite, 

 but is reduced by the cohering of the filings 



under the action of radiation to from 100 to 

 500 ohms. This allows a current to flow from 

 a local battery through a relay circuit in which 

 is a vibrating tapper and a sounder, or writer. 

 The former, tapping the coherer, restores the 

 high resistance by separating the filings. The 

 receiver is also supplied, either with the metal 

 strips and reflector or with the ground connec- 

 tion and vertical wire, according as the former 

 or the latter is used in the transmission. 



When the reflectors are used the ray within 

 which the signals can be received may be made 

 very narrow ; in one case at a distance of \^ 

 miles it was only about 100 feet. Marconi found 

 that horizontal wires were useless, and ac- 

 counted for this by the theory that the waves 

 from the vertical wire had a vertical plane of 

 polarization and were, therefore, not absorbed 

 by the surface of the earth. 



A number of installations have worked suc- 

 cessfully and without diflSculty for prolonged 

 intervals and in all sorts of weather. In one 

 case an 18-mile transmission was carried on 

 with an average of about one thousand words 

 per day. With the vertical wire transmitter, 

 hills seem to make little difference with the 

 transmission. In one case a distance of five 

 miles over land, with several intervening hills, 

 was successfully covered. 



F. C. C. 



BOTANICAL NOTES. 

 AN ELEMENTARY BOOK ON LICHENS. 



It is a hopeful sign when we find amply quali- 

 fied men engaging in the work of writing ele- 

 mentary text-books for the use of students in 

 the schools. It has been the duty of the writer 

 on more occasions than he has wished to 

 severely criticise books written for beginners by 

 those who themselves had but little knowledge 

 of the matter treated. It has been at once the 

 scandal and the weakness of the elementary 

 science text-books that they have too often con- 

 tained very little Science, for the very good rea- 

 son that their compilers were unacquainted with 

 Science. Some time ago Dr. Albert Schneider 

 published a large treatise on the lichens, which 

 at once proved his profound knowledge of the 

 subject as well as his ability to communicate it 

 clearly and forcibly. It is not necessary that 



